Write procedure using estimated best setting in first run

ABSTRACT

In one general embodiment, a method includes receiving a request for a write operation to be performed in a tape drive, determining an expected transaction size of a next write operation, comparing the expected transaction size of the next write operation to each of a first transaction size threshold and a second transaction size threshold in response to receiving the request, determining an optimum a write procedure based at least in part on the comparison, and invoking the optimum write procedure in response to determining the optimum write procedure, wherein the first transaction size threshold is greater than the second transaction size threshold, and wherein the optimum write procedure is selected from the group consisting of: a backhitch write procedure, a same wrap backhitchless flush (SWBF) write procedure, and a recursively accumulating backhitchless flush (RABF) write procedure.

RELATED APPLICATIONS

This application is a continuation of copending U.S. patent applicationSer. No. 13/449,219, filed Apr. 17, 2012; which is herein incorporatedby reference.

BACKGROUND

The present invention relates to data storage systems, and moreparticularly, this invention relates to using a best setting determinedaccording to select tape operating parameters during a write procedure(WP).

A tape drive is adapted to read and/or write data from/to a magnetictape using a range of tape speeds which are preset in the tape drive(for example, one tape drive may operate at 14 different tape speeds).Typically, write procedure performs a plurality of steps to accomplish awrite operation.

However, these steps are typically performed in a predetermined order,which is applied the same way in all cases, regardless of the tapecartridge, the tape cartridge/drive combination, and the circumstancessurrounding the write operation. Accordingly, it would be beneficial tohave a tape drive system that is capable of determining and invoking anoptimum write procedure according to a specific tape cartridge, tapecartridge/drive combination, and/or circumstances surrounding the writeoperation.

BRIEF SUMMARY

In one embodiment, a method includes: receiving a request for a writeoperation to be performed in a tape drive; determining an expectedtransaction size of a next write operation; comparing the expectedtransaction size of the next write operation to each of a firsttransaction size threshold and a second transaction size threshold inresponse to receiving the request; determining an optimum a writeprocedure based at least in part on the comparison; and invoking theoptimum write procedure in response to determining the optimum writeprocedure.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a tape drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., recording tape)over the magnetic head, and a controller electrically coupled to themagnetic head.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic diagram of a simplified tape drive systemaccording to one embodiment.

FIG. 2 illustrates a side view of a flat-lapped, bi-directional,two-module magnetic tape head according to one embodiment.

FIG. 2A is a tape bearing surface view taken from Line 2A of FIG. 2,according to one embodiment.

FIG. 2B is a detailed view taken from Circle 2B of FIG. 2A, according toone embodiment.

FIG. 2C is a detailed view of a partial tape bearing surface of a pairof modules, according to one embodiment.

FIG. 3 is a partial tape bearing surface view of a magnetic head havinga write-read-write configuration, according to one embodiment.

FIG. 4 is a partial tape bearing surface view of a magnetic head havinga read-write-read configuration, according to one embodiment.

FIG. 5 is a flowchart of a method, according to one embodiment.

FIG. 6 is a flowchart of a method, according to one embodiment.

FIG. 7 shows a schematic of a decision tree for determining an optimumwrite procedure, according to one embodiment.

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof.

In one general embodiment, a tape-based data storage system includes: aread channel; a write channel; logic configured to receiving a requestfor a write operation to be performed in a tape drive; logic configuredto determine an optimum a write procedure in response to receiving therequest, the determining being based on expected writing times of eachof a plurality of write procedures and an expected transaction size of anext write operation; and logic configured to invoke the determinedoptimum write procedure in response to determining the optimum writeprocedure.

In another general embodiment, a computer program product includesnon-transitory computer readable program code embodied on a computerreadable storage medium, the computer readable program code including:computer readable program code configured to receiving a request for awrite operation to be performed in a tape drive; computer readableprogram code configured to determine an expected transaction size of anext write operation; computer readable program code configured tocompare the expected transaction size of the next write operation toeach of a first transaction size threshold and a second transaction sizethreshold in response to receiving the request; computer readableprogram code configured to determine an optimum a write procedure basedat least in part on the comparison; and computer readable program codeconfigured to invoke the optimum write procedure in response todetermining the optimum write procedure.

In still another general embodiment, a method, includes: receiving arequest for a write operation to be performed in a tape drive;determining an expected transaction size of a next write operation;comparing the expected transaction size of the next write operation toeach of a first transaction size threshold and a second transaction sizethreshold in response to receiving the request; determining an optimum awrite procedure based at least in part on the comparison; and invokingthe optimum write procedure in response to determining the optimum writeprocedure.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as “logic,” a “circuit,” a “module,” ora “system.” Furthermore, aspects of the present invention may take theform of a computer program product embodied in one or more computerreadable medium(s) having computer readable program code embodiedthereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a non-transitory computer readable storage medium. Anon-transitory computer readable storage medium may be, for example, butnot limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. More specific examples (a non-exhaustivelist) of the computer readable storage medium would include thefollowing: a portable computer diskette, a hard disk, a random accessmemory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM or Flash memory), a portable compact discread-only memory (CD-ROM), an optical storage device, a magnetic storagedevice, or any suitable combination of the foregoing. In the context ofthis document, a computer readable storage medium may be anynon-transitory, tangible medium that can contain, or store a program foruse by or in connection with an instruction execution system, apparatus,or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device, such as anelectrical connection having one or more wires, an optical fiber, etc.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

FIG. 1 illustrates a simplified tape drive 100 of a tape-based datastorage system, which may be employed in the context of the presentinvention. While one specific implementation of a tape drive is shown inFIG. 1, it should be noted that the embodiments described herein may beimplemented in the context of any type of tape drive system.

As shown, a tape supply cartridge 120 and a take-up reel 121 areprovided to support a tape 122. One or more of the reels may form partof a removable cartridge and are not necessarily part of the system 100.The tape drive, such as that illustrated in FIG. 1, may further includedrive motor(s) to drive the tape supply cartridge 120 and the take-upreel 121 to move the tape 122 over a tape head 126 of any type. Suchhead may include an array of readers, writers, or both.

Guides 125 guide the tape 122 across the tape head 126. Such tape head126 is in turn coupled to a controller assembly 128 via a cable 130. Thecontroller 128 typically controls head functions such as servofollowing, writing, reading, etc. The controller may operate under logicknown in the art, as well as any logic disclosed herein. The cable 130may include read/write circuits to transmit data to the head 126 to berecorded on the tape 122 and to receive data read by the head 126 fromthe tape 122. An actuator 132 controls position of the head 126 relativeto the tape 122.

An interface 134 may also be provided for communication between the tapedrive and a host (integral or external) to send and receive the data andfor controlling the operation of the tape drive and communicating thestatus of the tape drive to the host, all as will be understood by thoseof skill in the art.

By way of example, FIG. 2 illustrates a side view of a flat-lapped,bi-directional, two-module magnetic tape head 200 which may beimplemented in the context of the present invention. As shown, the headincludes a pair of bases 202, each equipped with a module 204, and fixedat a small angle α with respect to each other. The bases may be“U-beams” that are adhesively coupled together. Each module 204 includesa substrate 204A and a closure 204B with a thin film portion, commonlyreferred to as a “gap” in which the readers and/or writers 206 areformed. In use, a tape 208 is moved over the modules 204 along a media(tape) bearing surface 209 in the manner shown for reading and writingdata on the tape 208 using the readers and writers. The wrap angle θ ofthe tape 208 at edges going onto and exiting the flat media supportsurfaces 209 are usually between about 0.1 degree and about 5 degrees.

The substrates 204A are typically constructed of a wear resistantmaterial, such as a ceramic. The closures 204B made of the same orsimilar ceramic as the substrates 204A.

The readers and writers may be arranged in a piggyback or mergedconfiguration. An illustrative piggybacked configuration comprises a(magnetically inductive) writer transducer on top of (or below) a(magnetically shielded) reader transducer (e.g., a magnetoresistivereader, etc.), wherein the poles of the writer and the shields of thereader are generally separated. An illustrative merged configurationcomprises one reader shield in the same physical layer as one writerpole (hence, “merged”). The readers and writers may also be arranged inan interleaved configuration. Alternatively, each array of channels maybe readers or writers only. Any of these arrays may contain one or moreservo track readers for reading servo data on the medium.

FIG. 2A illustrates the tape bearing surface 209 of one of the modules204 taken from Line 2A of FIG. 2. A representative tape 208 is shown indashed lines. The module 204 is preferably long enough to be able tosupport the tape as the head steps between data bands.

In this example, the tape 208 includes 4 to 22 data bands, e.g., with 16data bands and 17 servo tracks 210, as shown in FIG. 2A on a one-halfinch wide tape 208. The data bands are defined between servo tracks 210.Each data band may include a number of data tracks, for example 512 datatracks (not shown). During read/write operations, the readers and/orwriters 206 are positioned to specific track positions within one of thedata bands. Outer readers, sometimes called servo readers, read theservo tracks 210. The servo signals are in turn used to keep the readersand/or writers 206 aligned with a particular set of tracks during theread/write operations.

FIG. 2B depicts a plurality of readers and/or writers 206 formed in agap 218 on the module 204 in Circle 2B of FIG. 2A. As shown, the arrayof readers and writers 206 includes, for example, 16 writers 214, 16readers 216 and two servo readers 212, though the number of elements mayvary. Illustrative embodiments include 8, 16, 32, 40, and 64 readersand/or writers 206 per array. A preferred embodiment includes 32 readersper array and/or 32 writers per array, where the actual number oftransducing elements could be greater, e.g., 33, 34, etc. This allowsthe tape to travel more slowly, thereby reducing speed-induced trackingand mechanical difficulties and/or execute fewer “wraps” to fill or readthe tape. While the readers and writers may be arranged in a piggybackconfiguration as shown in FIG. 2B, the readers 216 and writers 214 mayalso be arranged in an interleaved configuration. Alternatively, eacharray of readers and/or writers 206 may be readers or writers only, andthe arrays may contain one or more servo readers 212. As noted byconsidering FIGS. 2 and 2A-B together, each module 204 may include acomplementary set of readers and/or writers 206 for such things asbi-directional reading and writing, read-while-write capability,backward compatibility, etc.

FIG. 2C shows a partial tape bearing surface view of complimentarymodules of a magnetic tape head 200 according to one embodiment. In thisembodiment, each module has a plurality of read/write (R/W) pairs in apiggyback configuration formed on a common substrate 204A and anoptional electrically insulative layer 236. The writers, exemplified bythe write head 214 and the readers, exemplified by the read head 216,are aligned parallel to a direction of travel of a tape mediumthereacross to form an R/W pair, exemplified by the R/W pair 222.

Several R/W pairs 222 may be present, such as 8, 16, 32 pairs, etc. TheR/W pairs 222 as shown are linearly aligned in a direction generallyperpendicular to a direction of tape travel thereacross. However, thepairs may also be aligned diagonally, etc. Servo readers 212 arepositioned on the outside of the array of R/W pairs, the function ofwhich is well known.

Generally, the magnetic tape medium moves in either a forward or reversedirection as indicated by arrow 220. The magnetic tape medium and headassembly 200 operate in a transducing relationship in the mannerwell-known in the art. The piggybacked MR head assembly 200 includes twothin-film modules 224 and 226 of generally identical construction.

Modules 224 and 226 are joined together with a space present betweenclosures 204B thereof (partially shown) to form a single physical unitto provide read-while-write capability by activating the writer of theleading module and reader of the trailing module aligned with the writerof the leading module parallel to the direction of tape travel relativethereto. When a module 224, 226 of a piggyback head 200 is constructed,layers are formed in the gap 218 created above an electricallyconductive substrate 204A (partially shown), e.g., of AlTiC, ingenerally the following order for the R/W pairs 222: an insulating layer236, a first shield 232 typically of an iron alloy such as NiFe(permalloy), CZT or Al—Fe—Si (Sendust), a sensor 234 for sensing a datatrack on a magnetic medium, a second shield 238 typically of anickel-iron alloy (e.g., 80/20 Permalloy), first and second writer poletips 228, 230, and a coil (not shown).

The first and second writer poles 228, 230 may be fabricated from highmagnetic moment materials such as 45/55 NiFe. Note that these materialsare provided by way of example only, and other materials may be used.Additional layers such as insulation between the shields and/or poletips and an insulation layer surrounding the sensor may be present.Illustrative materials for the insulation include alumina and otheroxides, insulative polymers, etc.

The configuration of the tape head 126 according to one embodimentincludes multiple modules, preferably three or more. In awrite-read-write (W-R-W) head, outer modules for writing flank one ormore inner modules for reading. Referring to FIG. 3, depicting a W-R-Wconfiguration, the outer modules 402, 406 each include one or morearrays of writers 410. The inner module 404 of FIG. 3 includes one ormore arrays of readers 408 in a similar configuration. Variations of amulti-module head include a R-W-R head (FIG. 4), a R-R-W head, a W-W-Rhead, etc. In yet other variations, one or more of the modules may haveread/write pairs of transducers. Moreover, more than three modules maybe present. In further approaches, two outer modules may flank two ormore inner modules, e.g., in a W-R-R-W, a R-W-W-R arrangement, etc. Forsimplicity, a W-R-W head is used primarily herein to exemplifyembodiments of the present invention. One skilled in the art apprisedwith the teachings herein will appreciate how permutations of thepresent invention would apply to configurations other than a W-R-Wconfiguration.

In a tape drive system, upon receiving a write request, such as during async operation between the tape drive system and a host system, the tapedrive system must determine a WP for writing the data to the tape.

Several of the conventional approaches to improving tape drive systemperformance as understood herein include backhitch WPs, same wrapbackhitchless flush (SWBF) WPs such as disclosed in U.S. Pat. No.7,903,363, incorporated herein by reference, and recursivelyaccumulating backhitchless flush (RABF) WPs such as disclosed in U.S.Pat. No. 6,856,479, incorporated herein by reference, among otherequivalent WPs as would be understood by one having ordinary skill inthe art upon reading the present descriptions.

For example, WPs may be employed to improve tape drive systemperformance via maximizing a tape drive storage capacity, maximizing atape drive write operation fidelity, minimizing a tape drive storagecapacity degradation, minimizing a tape drive write operation time, etc.as would be understood by one having ordinary skill in the art uponreading the present descriptions.

As understood herein, a data storage system may be characterized byseveral performance attributes, including an ideal data capacity, anactual data capacity, a capacity margin, a capacity margin ratio, etc.as would be understood by one having ordinary skill in the art uponreading the present descriptions.

In one embodiment, the ideal data capacity may represent a typical oraverage maximum data capacity for a particular type of storage systemand be reported in a data size unit such as megabytes (MB), gigabytes(GB), terabytes (TB), etc. as would be understood by one having ordinaryskill in the art upon reading the present descriptions. Furthermore, theideal data capacity may be the average or typical storage capacityavailable to a user, and may be the data capacity reported to the useras the total storage system capacity.

Similarly, the actual data capacity may represent an actual maximum datacapacity for a particular type of storage system as observed in practicewhen performing writes with a very low error rate, in some approaches.As with the ideal data capacity, the actual data capacity may bereported in a data size unit such as megabytes (MB), gigabytes (GB),terabytes (TB), etc. as would be understood by one having ordinary skillin the art upon reading the present descriptions.

In additional embodiments, the capacity margin may represent adifference between the actual data capacity for a particular storagesystem and the ideal data capacity for the particular storage system. Aswith the actual data capacity and the ideal data capacity, the capacitymargin may be reported in a data size unit such as megabytes (MB),gigabytes (GB), terabytes (TB), etc. as would be understood by onehaving ordinary skill in the art upon reading the present descriptions.

Furthermore, the capacity margin ratio may represent a relativecomparison of the capacity margin and the actual data capacity for aparticular storage system. The capacity margin ratio may be reported asa ratio, a percentage, a fraction, etc. as would be understood by onehaving ordinary skill in the art upon reading the present descriptions.

Both capacity margin and capacity margin ratio may represent datastorage system performance metrics that are informative regarding theexpected and observed error rate and thus overall performance of aparticular data storage system in terms of write operation effectivenessand efficiency, among other qualities, as will be appreciated by theskilled artisan reading the present descriptions.

SWBF, RABF, and backhitching WPs may provide improved writing for datastorage systems and therefore improve overall system performance,especially over a series of data sync operations between a hosttransferring data and the data storage system receiving the data forstorage. Moreover, each WP offers unique advantages and improvements tothe data storage system. For example, backhitching is usually a slowerWP with respect to write operation speed than either SWBF or RABF, whichmay result in slower system performance, but offers the advantage thatlittle or no data capacity may be lost when utilizing backhitching WPs.

On the other hand, SWBF and RABF are usually characterized by fast writeoperation speeds relative to backhitching, conferring correspondinglyfaster performance to the storage system. However, SWBF accomplishesfaster performance by skipping portions of the storage capacity inresponse to receiving a request for a write operation to be performed ina tape drive, and accordingly sacrifices storage capacity with eachwrite to the detriment of overall storage capacity for the data storagesystem utilizing SWBF.

RABF is also often characterized by fast write operation speeds relativeto backhitching, but is often slower than SWBF. RABF writes datatemporarily in a reserved tape area, skipping some portion of storagecapacity, but recursively writes to the original tape area withoutskipping the portion of storage capacity. Therefore, RABF does notcauses capacity loss, in some approaches.

In general, RABF is better method than SWBF if write operations arefrequently requested for small data transfer transactions. If syncoperation is not so frequently, SWBF is better method than RABF, sincethe skipping portion by SWBF is not so affect to the total writtencapacity.

As will be understood by one having ordinary skill in the art uponreading the present descriptions, the above-described WPs may conferimprovements to data storage system performance, but each WP carries anassociated cost to performance, and therefore it is desirable andadvantageous to devise intelligent implementations of the WPs in unisonand/or combination to maximize data storage system performance accordingto the specific needs of a given user, storage facility, storage serviceprovider, etc.

Accordingly, the present descriptions detail several embodiments of aninventive implementation for WPs such as backhitch, SWBF, RABF, etc. aswould be understood by one having ordinary skill in the art upon readingthe present descriptions. At a high-level, the presently disclosedsystems and methods achieve an improved WP performance and confercorresponding improvements to data storage system performance bydetermining an optimum WP for a given write operation based on one ormore of several factors, including an expected transaction size of asubsequent write operation, a capacity margin of a data storage system,an expected writing time for one of more WPs, an expected time remaininguntil data for the subsequent write operation are ready to write to thedata storage system, etc. as would be understood by one having ordinaryskill in the art upon reading the present descriptions.

If a transaction requiring writing is a large transaction, and/or if anext transaction scheduled for writing subsequent to writing is a largetransaction, backhitching would be expected to take a long time tocomplete writing to the detriment of overall system performance.Accordingly, conventionally SWBF has been utilized to improve systemperformance for WP on or in the vicinity of large transactions.Surprisingly, however, the inventors of the presently disclosed systemsand methods discovered that, even if a transaction is a largetransaction, SWBF is not always the best method for WP from aperformance perspective. In particular, in systems where a tape ismoving at a relatively slow speed, e.g. to avoid emptying the buffer,SWBF creates more overhead than normal backhitching WPs and fails toconfer the typical performance advantages of SWBF WP. Accordingly, insome circumstances backhitch is unexpectedly the superior performing WPfrom both write speed and data capacity loss perspectives.

To this effect the present descriptions disclose a new methodology forselecting optimum WP for a variety of circumstances and with thesurprising insight that normal backhitching or other procedure mayconfer superior WP and data storage performance for a given set ofconditions, even in large transaction sizes. In some approaches the newmethodology may determine an optimum WP based on at least the expectedtransaction size for the next write operation and the expected timeremaining until a next transaction is ready for writing. Moreover, theexpected transaction size may be compared to one or more thresholds tofurther define the appropriate optimum WP according to expectedtransaction size.

In some approaches, an expected transaction size for the next writeoperation may comprise an estimated transaction size based on an averagetransaction size of one or more previous transactions. In preferredembodiments, the expected transaction size for the next write operationmay be an average of two, three or four immediately previous transactionsizes.

Moreover, the presently described systems and methods may employ one ormore thresholds against which to compare one or more of theabove-described factors to assist in determining which WP would beoptimal for a given write operation under the particular circumstancesof the write and/or the data storage environment. In several approaches,a plurality of transaction size thresholds may be employed, and a firsttransaction size threshold may represent a boundary between large andmid-sized transactions. Moreover, a second transaction size thresholdmay represent a boundary between mid and small-sized transactions, insome approaches. Such thresholds may be predefined for a given driveand/or media type, selected by a user, programmed into the drive, etc.

Furthermore, several exemplary comparisons between thresholds and theabove-described factors are disclosed herein. As would be understood byone having ordinary skill in the art upon reading the presentdescriptions, each of the comparisons may be performed according to avariety of criteria. For example, a condition may be satisfied where afactor value is greater than a threshold, greater than or equal to athreshold, equal to a threshold, less than a threshold, or less than orequal to a threshold, in various approached.

As understood herein, an “optimum” WP may be understood to represent anWP that accomplishes superior performance improvements for a datastorage system undergoing one or more write operations. Superiorperformance may be defined according to any measure desired or requiredby a given user, storage system, storage service provider, etc. as wouldbe understood by one having ordinary skill in the art upon reading thepresent descriptions.

For example, in some embodiments high-speed performance may be preferredover efficient data capacity usage, and the presently described systemsand methods may select the “optimum” WP that provides maximum writeoperation speed. In other approaches, efficient use of data capacity maybe preferred over write operation speed, and the presently describedsystems and methods may select the “optimum” WP that provides maximumefficiency to data capacity usage. Of course, other performancecharacteristics may be preferred in different situations and thepresently disclosed systems and methods may be optimized to providedesired data storage system performance in terms of each of a variety ofperformance characteristics as would be understood by one havingordinary skill in the art upon reading the present descriptions.

According to one embodiment, a tape drive system includes: a readchannel; a write channel; logic configured to receive a request for awrite operation; logic configured to determine an optimum a WP inresponse to receiving the request, the determining being based onexpected writing times of each of a plurality of WPs and an expectedtransaction size of a next write operation; and logic configured toinvoke the determined optimum WP in response to determining the optimumWP.

Preferably, the determining is based on expected writing times relativeto two thresholds. In some embodiments, the two thresholds may include afirst transaction size threshold and a second transaction sizethreshold. In preferred embodiments, the first transaction sizethreshold is greater than the second transaction size threshold.

Moreover, in additional embodiments invoking the optimum WP mayeffectively maintain a capacity margin ratio of about 10% or less, andin preferred embodiments a capacity margin ratio of about 7% or less.

In more embodiments, the logic configured to determine the optimum WPmay include logic configured to determine a capacity margin ratio; logicconfigured to determine the expected transaction size of the next writeoperation; logic configured to calculate the expected writing time foreach of the plurality of WPs, each WP being selected from a groupconsisting of: a backhitch WP, a same wrap backhitchless flush (SWBF)WP, and a recursively accumulating backhitchless flush (RABF) WP; andlogic configured to determine an expected time remaining until the nextwrite operation, where determining the optimum WP is further based onthe expected time remaining until the next write operation.

In still more embodiments, the SWBF WP may be selected as the optimum WPin response to the following conditions being satisfied: the expectedtransaction size of the next write operation is greater than a firsttransaction size threshold; the SWBF WP expected writing time is lessthan the backhitch WP expected writing time; the expected time remaininguntil the next write operation is less than the SWBF WP expected writingtime; and the capacity margin ratio is greater than a predeterminedvalue.

In some embodiments, the predetermined value may be a value determinedto be adequate for the SWBF WP for the given drive and/or tape; aselected value such as 10%, 7%, etc. as would be understood by onehaving ordinary skill in the art upon reading the present descriptions.Moreover, one advantage of such embodiments is that data will be readyin time for SWBF to save time, and SWBF sufficiently faster thanbackhitch to justify SWBF in view of capacity margin to save write time.This embodiment also saves time/processing power by omitting any furthercomparison between SWBF, RABF and backhitch WPs.

In further embodiments, the SWBF WP may be selected as the optimum WP inresponse to the following conditions being satisfied: the expectedtransaction size of the next write operation is less than a firsttransaction size threshold and greater than a second transaction sizethreshold; the expected time remaining until the next write operation isless than the SWBF WP expected writing time; and the capacity marginratio is greater than a predetermined value.

According to such embodiments, data will be ready in time for SWBF tosave time, and SWBF is sufficiently faster than backhitch to justifySWBF in view of capacity margin to save write time. Such embodimentsalso save time/processing power by omitting any further comparisonbetween SWBF, RABF and backhitch WPs.

Furthermore, in some approaches the RABF WP may be selected as theoptimum WP in response to the transaction size of the next writeoperation being less than a second transaction size threshold becauseRABF WP is surprisingly faster than normal backhitch WP for smalltransactions.

Moreover, in additional and/or alternative approaches the RABF WP may beselected as the optimum WP in response to the following conditions beingsatisfied: the expected transaction size of the next write operation isless than a first transaction size threshold and greater than a secondtransaction size threshold; and the capacity margin ratio is less than apredetermined value.

Moreover still the RABF WP may be selected as the optimum WP in responseto the following conditions being satisfied, according to oneembodiment: the expected transaction size of the next write operation isless than a first transaction size threshold and greater than a secondtransaction size threshold; the expected time remaining until the nextwrite operation is greater than the SWBF WP expected writing time; andthe capacity margin ratio is greater than a predetermined value. In oneapproach, the backhitch WP is selected as the optimum WP in response tothe following conditions being satisfied: the expected transaction sizeof the next write operation is greater than a first transaction sizethreshold; the SWBF expected writing time of the next write operation isgreater than the backhitch WP expected writing time; and the capacitymargin ratio is greater than a predetermined value.

In another approach, the backhitch WP is selected as the optimum WP inresponse to the following conditions being satisfied: the expectedtransaction size of the next write operation is greater than a firsttransaction size threshold; the SWBF expected writing time of the nextwrite operation is less than the backhitch WP expected writing time; thecapacity margin ratio is greater than a predetermined value; and theexpected time remaining until the next write operation is greater thanthe SWBF WP expected writing time.

The presently systems may also be embodied as a data storage system,including a tape drive system as described in any of the embodimentsherein; a drive mechanism for passing a magnetic medium over a magnetichead; and a controller electrically coupled to the magnetic head.

Referring now to FIG. 5, a method 500 is shown, according to oneembodiment. As described and understood herein, the method 500 may beperformed in any suitable environment, including the environments ofFIGS. 1-4, among others.

In one embodiment, method 500 includes operation 502, where a requestfor a write operation to be performed in a tape drive is received.

In operation 504, an expected transaction size of a next write operationis determined.

In operation 506, the expected transaction size of the next writeoperation is compared to each of a first transaction size threshold anda second transaction size threshold in response to receiving therequest.

In operation 508, an optimum a WP is determined based at least in parton the comparison in operation 506.

In operation 510, the optimum WP is invoked in response to determiningthe optimum WP in operation 508.

According to some embodiments of the presently disclosed systems andmethods, the first transaction size threshold may be greater than thesecond transaction size threshold, and the optimum WP may be selectedfrom among a backhitch WP, a same wrap backhitchless flush (SWBF) WP,and a recursively accumulating backhitchless flush (RABF) WP.

In some embodiments, a tape drive performing the write operationmaintains a capacity margin ratio of less than 10%, preferably less thanabout 7.0% by invoking the optimum WP.

Referring now to FIG. 6, a method 600 is shown, according to oneembodiment. As described and understood herein, the method 600 may beperformed in any suitable environment, including the environments ofFIGS. 1-4, among others.

In one embodiment, method 600 further defines the methodology fordetermining the optimum WP. For example, in one embodiment determiningthe optimum WP may include operation 602, where a capacity margin ratiois determined, e.g. a capacity margin ratio of the tape drive performingthe write operation.

In operation 604, an expected writing time is calculated for each of thebackhitch WP, the SWBF WP, and the RABF WP.

In operation 606, an expected time remaining until the next writeoperation is determined.

In operation 608, where the optimum WP is selected based on at least oneof: the backhitch WP expected writing time, the SWBF WP expected writingtime, the RABF WP expected writing time, the expected transaction sizeof the next write operation, the capacity margin ratio, and the expectedtime remaining until the next write operation

Referring now to FIG. 7, an exemplary decision tree 700 according to oneimplementation of the presently disclosed systems and methods is shown.In general, improved writing and correspondingly improved data storagesystem performance may be conferred by employing decision tree 700 invarious approaches.

As shown in FIG. 7, upon receiving a request for a write operation to beperformed in a tape drive at start point 701, an expected transactionsize T(x) is compared to a first transaction size threshold T(a) indecision point 702. If the expected transaction size is larger than thefirst transaction size threshold, this indicates that the transaction isa “large transaction,” and the analysis continues by determining whethera capacity margin CM of a data storage system is greater than a minimumcapacity margin CM(low) required to support SWBF WP in decision point704.

If the capacity margin is insufficient to support SWBF WP, then theanalysis concludes that normal backhitch WP BH is the optimum WP underthe circumstances in conclusion point 706. Otherwise, the capacitymargin is insufficient to support SWBF WP, then the analysis continuesby determining whether SWBF WP is expected to be faster than normalbackhitch WP in decision point 708. In some approaches, thisdetermination may be made according to the calculated expected elapsedtime for each WP substantially as disclosed in U.S. Pat. Nos. 7,710,681and 8,035,912.

As would be understood by one having ordinary skill in the art uponreading the present descriptions, the advantage of SWBF relative tonormal backhitch writing is that SWBF is faster, but the increased speedcomes at a price of lost capacity. Accordingly, upon receiving a requestfor a write operation, utilizing SWBF to perform the write willunnecessarily sacrifice data capacity without conferring any speedadvantage if backhitch writing is faster than SWBF under thecircumstances. Accordingly, in such situations normal backhitch writingmay be preferred in order to maximize storage capacity and write speedperformance. In one embodiment, where SWBF WP is expected to be slowerthan backhitch WP, then backhitch WP is chosen as the optimum WP underthe circumstances such as shown in conclusion point 710 of FIG. 7.

Alternatively, if SWBF WP is determined to be faster than backhitch WPin decision point 708, then the analysis continues by determiningwhether the next transaction will be ready for writing before SWBF WP isexpected to complete writing in decision point 712. If the nexttransaction will be ready for subsequent writing before SWBF WP isexpected to complete writing, then the analysis concludes that SWBF WPis the optimum WP under the circumstances as shown in conclusion point716. Otherwise, if the next transaction will not be ready for subsequentwriting before SWBF WP is expected to complete writing, then theanalysis concludes that backhitch WP is the optimum WP under thecircumstances as shown in conclusion point 714.

As will be appreciated by the skilled artisan reading the presentdescriptions, even if a transaction is large, sufficient capacity marginexists to support SWBF WP, and SWBF WP is expected to be faster thanbackhitch WP, unnecessary data capacity loss will occur if SWBF WP isselected as the optimum WP but data would not be ready for subsequentwriting for an amount of time greater than the expected SWBF WP writetime, especially if the data would not be ready for subsequent writingfor an amount of time greater than the expected backhitch WP write time.This is because, in the first instance, SWBF would sacrifice capacityand finish writing before the next data are ready for writing, and thesystem would sit idly for the interim. In the second instance, SWBFwould sacrifice capacity where backhitch would not, and both WPs wouldcomplete before the next data are ready for subsequent writing,resulting in a complete waste of capacity with no corresponding gain inwrite performance.

If the transaction is determined not to be a “large transaction” indecision point 702, the expected transaction size is compared to asecond transaction size threshold T(b) in decision point 718. If theexpected transaction size is less than the second transaction sizethreshold, this indicates that the transaction is a “small” transactionand the analysis concludes that RABF WP is the optimum WP under thecircumstances as shown in conclusion point 720 of FIG. 7.

On the other hand, if the expected transaction size is larger than thesecond transaction size threshold but less than the first transactionsize threshold, this indicates that the transaction is a “mid-sized”transaction and the analysis continues by determining whether a capacitymargin CM of a data storage system is greater than a minimum capacitymargin CM(low) required to support SWBF WP in decision point 722. If thecapacity margin of the data storage system is insufficient to supportSWBF, then the analysis concludes that RABF WP is the optimum WP underthe circumstances as shown in conclusion point 724 of FIG. 7.

Otherwise, if the capacity margin CM of a data storage system is greaterthan a minimum capacity margin CM(low) required to support SWBF WP, thenthe analysis continues by determining whether the next transaction willbe ready for writing before SWBF WP is expected to complete writing indecision point 726. If the next transaction will be ready for subsequentwriting before SWBF WP is expected to complete writing, then theanalysis concludes that SWBF WP is the optimum WP under thecircumstances as shown in conclusion point 728. Otherwise, if the nexttransaction will not be ready for subsequent writing before SWBF WP isexpected to complete writing, then the analysis concludes that RABF WPis the optimum WP under the circumstances as shown in conclusion point730.

The decision tree 700 shown in FIG. 7 may also be represented asmicro-code containing nested logic statements as shown below, in oneembodiment.

If (Tx size >= Tx_Threshold_A ) { If (capacity margin is sufficient forSWBF ) { If (SWBF is faster than Normal Backhitch Writing ) { If ( nextdata is available within the remaining time ) −> Write with SWBF else {−> Write with backhitch.} else { −> Write with backhitch } else{ −>Write with backhitch } } else if ( Tx size >= Tx_Threshold_B) { If(capacity margin is sufficient for SWBF ){ If ( next data is availablewithin the remaining time ){ −> Write with SWBF} else { −> Write withRABF} else { −> Write with RABF} else if ( Tx size < Tx_Threshold_B ){−> Write with RABF} }

It will be clear that the various features of the foregoingmethodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will also be clear to one skilled in the art that the methodology ofthe present invention may suitably be embodied in a logic apparatuscomprising logic to perform various steps of the methodology presentedherein, and that such logic may comprise hardware components or firmwarecomponents.

It will be equally clear to one skilled in the art that the logicarrangement in various approaches may suitably be embodied in a logicapparatus comprising logic to perform various steps of the method, andthat such logic may comprise components such as logic gates in, forexample, a programmable logic array. Such a logic arrangement mayfurther be embodied in enabling means or components for temporarily orpermanently establishing logical structures in such an array using, forexample, a virtual hardware descriptor language, which may be storedusing fixed or transmittable carrier media.

It will be appreciated that the methodology described above may alsosuitably be carried out fully or partially in software running on one ormore processors (not shown), and that the software may be provided as acomputer program element carried on any suitable data carrier (also notshown) such as a magnetic or optical computer disc. The channels for thetransmission of data likewise may include storage media of alldescriptions as well as signal carrying media, such as wired or wirelesssignal media.

Embodiments of the present invention may suitably be embodied as acomputer program product for use with a computer system. Such animplementation may comprise a series of computer readable instructionseither fixed on a tangible medium, such as a computer readable medium,for example, diskette, CD-ROM, ROM, or hard disk, or transmittable to acomputer system, via a modem or other interface device, over either atangible medium, including but not limited to optical or analoguecommunications lines, or intangibly using wireless techniques, includingbut not limited to microwave, infrared or other transmission techniques.The series of computer readable instructions embodies all or part of thefunctionality previously described herein.

For example, in one embodiment the inventive computer program product asdisclosed herein may be a computer program product comprisingnon-transitory computer readable program code embodied on a computerreadable storage medium, the computer readable program code includingcomputer readable program code configured to receive a request for awrite operation to be performed in a tape drive by a tape drive;computer readable program code configured to determine an expectedtransaction size of a next write operation; computer readable programcode configured to compare the expected transaction size of the nextwrite operation to each of a first transaction size threshold and asecond transaction size threshold in response to receiving the request;computer readable program code configured to determine an optimum a WPbased at least in part on the comparison; and computer readable programcode configured to invoke the optimum WP in response to determining theoptimum WP, where the first transaction size threshold is greater thanthe second transaction size threshold, and where the optimum WP isselected from the group consisting of: a backhitch WP, a same wrapbackhitchless flush (SWBF) WP, and a recursively accumulatingbackhitchless flush (RABF) WP.

Those skilled in the art will appreciate that such computer readableinstructions can be written in a number of programming languages for usewith many computer architectures or operating systems. Further, suchinstructions may be stored using any memory technology, present orfuture, including but not limited to, semiconductor, magnetic, oroptical, or transmitted using any communications technology, present orfuture, including but not limited to optical, infrared, or microwave. Itis contemplated that such a computer program product may be distributedas a removable medium with accompanying printed or electronicdocumentation, for example, shrink-wrapped software, pre-loaded with acomputer system, for example, on a system ROM or fixed disk, ordistributed from a server or electronic bulletin board over a network,for example, the Internet or World Wide Web.

Communications components such as input/output or I/O devices (includingbut not limited to keyboards, displays, pointing devices, etc.) can becoupled to the system either directly or through intervening I/Ocontrollers.

Communications components such as buses, interfaces, network adapters,etc. may also be coupled to the system to enable the data processingsystem, e.g., host, to become coupled to other data processing systemsor remote printers or storage devices through intervening private orpublic networks. Modems, cable modem and Ethernet cards are just a fewof the currently available types of network adapters.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer to offer service on demand.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A method, comprising: receiving a request for awrite operation to be performed in a tape drive; determining an expectedtransaction size of a next write operation; comparing the expectedtransaction size of the next write operation to each of a firsttransaction size threshold and a second transaction size threshold inresponse to receiving the request; determining an optimum a writeprocedure based at least in part on the comparison; and invoking theoptimum write procedure in response to determining the optimum writeprocedure, wherein the first transaction size threshold is greater thanthe second transaction size threshold, and wherein the optimum writeprocedure is selected from the group consisting of: a backhitch writeprocedure, a same wrap backhitchless flush (SWBF) write procedure, and arecursively accumulating backhitchless flush (RABF) write procedure. 2.The method as recited in claim 1, wherein determining the optimum writeprocedure comprises: determining a capacity margin ratio; calculating anexpected writing time for each of the backhitch write procedure, theSWBF write procedure, and the RABF write procedure; determining anexpected time remaining until the next write operation; and selectingthe optimum write procedure based on at least one of: the backhitchwrite procedure expected writing time, the SWBF write procedure expectedwriting time, the RABF write procedure expected writing time, theexpected transaction size of the next write operation, the capacitymargin ratio, and the expected time remaining until the next writeoperation.
 3. The method as recited in claim 2, wherein the SWBF writeprocedure is selected as the optimum write procedure when: the expectedtransaction size of the next write operation is greater than the firsttransaction size threshold; the SWBF write procedure expected writingtime is less than the backhitch write procedure expected writing time;the expected time remaining until the next write operation is less thanthe SWBF write procedure expected writing time; and the capacity marginratio is greater than a predetermined value.
 4. The method as recited inclaim 2, wherein the SWBF write procedure is selected as the optimumwrite procedure in response to the following conditions being satisfied:the expected transaction size of the next write operation is less thanthe first transaction size threshold and greater than the secondtransaction size threshold; the expected time remaining until the nextwrite operation is less than the SWBF write procedure expected writingtime; and the capacity margin ratio is greater than a predeterminedvalue.
 5. The method as recited in claim 2, wherein the RABF writeprocedure is selected as the optimum write procedure in response to thefollowing conditions being satisfied: the expected transaction size ofthe next write operation is less than the first transaction sizethreshold and greater than the second transaction size threshold; andthe capacity margin ratio is less than a predetermined value.
 6. Themethod as recited in claim 2, wherein the RABF write procedure isselected as the optimum write procedure in response to the followingconditions being satisfied: the expected transaction size of the nextwrite operation is less than the first transaction size threshold andgreater than the second transaction size threshold; the expected timeremaining until the next write operation is greater than the SWBF writeprocedure expected writing time; and the capacity margin ratio isgreater than a predetermined value.
 7. The method as recited in claim 2,wherein the backhitch write procedure is selected as the optimum writeprocedure in response to the following conditions being satisfied: theexpected transaction size of the next write operation is greater thanthe first transaction size threshold; the SWBF expected writing time ofthe next write operation is greater than the backhitch write procedureexpected writing time; and the capacity margin ratio is greater than apredetermined value.
 8. The method as recited in claim 2, wherein thebackhitch write procedure is selected as the optimum write procedure inresponse to the following conditions being satisfied: the expectedtransaction size of the next write operation is greater than the firsttransaction size threshold; the SWBF expected writing time of the nextwrite operation is less than the backhitch write procedure expectedwriting time; the capacity margin ratio is greater than as predeterminedvalue; and the expected time remaining until the next write operation isgreater than the SWBF write procedure expected writing time.
 9. Amethod, comprising: receiving a request for a write operation to beperformed in a tape drive; determining an optimum a write procedure inresponse to receiving the request, the determining comprising:determining a capacity margin ratio; determining an expected transactionsize of a next write operation; calculating an expected writing time foreach of a backhitch write procedure, a same wrap backhitchless flush(SWBF) write procedure, and a recursively accumulating backhitchlessflush (RABF) write procedure; determining a expected time remaininguntil the next write operation; and selecting the optimum writeprocedure based on at least one of: the backhitch write procedureexpected writing time, the SWBF write procedure expected writing time,the RABF write procedure expected writing time, the expected transactionsize of the next write operation, the capacity margin ratio, and theexpected time remaining until the next write operation; and invoking theoptimum write procedure based on the selection, wherein the SWBF writeprocedure is selected as the optimum write procedure in response to oneof the following sets of conditions being satisfied: the expectedtransaction size of the next write operation is greater than the firsttransaction size threshold, the SWBF write procedure expected writingtime is less than the backhitch write procedure expected writing time,the expected time remaining until the next write operation is less thanthe SWBF write procedure expected writing time and the capacity marginratio is greater than about 7.0%; and the expected transaction size ofthe next write operation is less than the first transaction sizethreshold and greater than the second transaction size threshold, theSWBF write procedure expected writing time is less than the backhitchwrite procedure expected writing time, the expected time remaining untilthe next write operation is less than the SWBF write procedure expectedwriting time and the capacity margin ratio is greater than about 7.0%,wherein the RABF write procedure is selected as the optimum writeprocedure in response to one of the following conditions beingsatisfied: the expected transaction size of the next write operation isless than the second transaction size threshold; the expectedtransaction size of the next write operation is less than the firsttransaction size threshold and greater than the second transaction sizethreshold and the capacity margin ratio is less than about 7.0%; and theexpected transaction size of the next write operation is less than thefirst transaction size threshold and greater than the second transactionsize threshold, the expected time remaining until the next writeoperation is greater than the SWBF write procedure expected writing timeand the capacity margin ratio is greater than about 7.0%, and whereinthe backhitch write procedure is selected as the optimum write procedurein response to one of the following conditions being satisfied: theexpected transaction size of the next write operation is greater thanthe first transaction size threshold and the capacity margin ratio isless than about 7.0%; the expected transaction size of the next writeoperation is greater than the first transaction size threshold, the SWBFexpected writing time of the next write operation is greater than thebackhitch write procedure expected writing time and the capacity marginratio is greater than about 7.0%; and the expected transaction size ofthe next write operation is greater than the first transaction sizethreshold, the SWBF expected writing time of the next write operation isless than the backhitch write procedure expected writing time, thecapacity margin ratio is greater than about 7.0% and the expected timeremaining until the next write operation is greater than the SWBF writeprocedure expected writing time.
 10. The method as recited in claim 2,wherein the capacity margin ratio is characterized by a value in a rangefrom 0% to 100%, and wherein invoking the optimum write proceduremaintains the value of the capacity margin ratio below about 10%. 11.The method as recited in claim 2, wherein the capacity margin ratio is aratio between a capacity margin of the tape drive and an actual datacapacity of the tape drive.
 12. The method as recited in claim 11,wherein the capacity margin is a difference between an actual datacapacity of the tape drive and an ideal data capacity of the tape drive.13. The method as recited in claim 1, wherein at least one of the firsttransaction size threshold and the second transaction size threshold isbased on one or more factors selected from: a drive type correspondingto the tape drive; a media type corresponding to the tape drive; auser-defined value; and a predefined value programmed into the tapedrive.
 14. The method as recited in claim 1, wherein the expectedtransaction size of the next write operation comprises an average of atleast two immediately previous transaction sizes.
 15. The method asrecited in claim 1, wherein the optimum write procedure is determinedfrom among a plurality of candidate write procedures, wherein theoptimum write procedure is characterized by a minimum tape drive storagecapacity degradation, and wherein each candidate write procedure ischaracterized by a tape drive storage capacity degradation greater thanthe minimum tape drive storage capacity degradation.
 16. The method asrecited in claim 1, wherein the optimum write procedure is determinedfrom among a plurality of candidate write procedures, wherein theoptimum write procedure is characterized by a maximum data usageefficiency, and wherein each candidate write procedure is characterizedby a data usage efficiency less than the maximum data usage efficiency.17. The method as recited in claim 1, wherein the optimum writeprocedure is determined from among a plurality of candidate writeprocedures, wherein the optimum write procedure is characterized by amaximum write operation speed, and wherein each candidate writeprocedure is characterized by a write operation speed less than themaximum write operation speed.
 18. The method as recited in claim 1,wherein the optimum write procedure is determined from among a pluralityof candidate write procedures, wherein the optimum write procedure ischaracterized by at least two of: a maximum data usage efficiency; amaximum write operation speed; and a minimum tape drive storage capacitydegradation, and wherein each candidate write procedure is characterizedby at least two of: a data usage efficiency less than the maximum datausage efficiency, a write operation speed less than the maximum writeoperation speed; and a tape drive storage capacity degradation greaterthan the minimum tape drive storage capacity degradation.
 19. The methodas recited in claim 18, wherein determining the optimum write procedurecomprises: determining a capacity margin ratio; calculating an expectedwriting time for each of the backhitch write procedure, the SWBF writeprocedure, and the RABF write procedure; determining an expected timeremaining until the next write operation; and selecting the optimumwrite procedure based on at least one of: the backhitch write procedureexpected writing time, the SWBF write procedure expected writing time,the RABF write procedure expected writing time, the expected transactionsize of the next write operation, the capacity margin ratio, and theexpected time remaining until the next write operation, wherein thecapacity margin ratio is a ratio between a capacity margin of the tapedrive and an actual data capacity of the tape drive, wherein thecapacity margin is a difference between an actual data capacity of thetape drive and an ideal data capacity of the tape drive, wherein thecapacity margin ratio is characterized by a value in a range from 0% to100%, wherein invoking the optimum write procedure maintains the valueof the capacity margin ratio below about 10%, wherein at least one ofthe first transaction size threshold and the second transaction sizethreshold is based on one or more factors selected from: a drive typecorresponding to the tape drive; a media type corresponding to the tapedrive; a user-defined value; and a predefined value programmed into thetape drive, and wherein the expected transaction size of the next writeoperation comprises an average of at least two immediately previoustransaction sizes.
 20. A method, comprising: receiving a request for awrite operation to be performed in a tape drive; determining an optimuma write procedure from among a plurality of candidate write procedures,the plurality of candidate write procedures comprising: a backhitch (BH)write procedure, a same wrap backhitchless flush (SWBF) write procedure,and a recursively accumulating backhitchless flush (RABF) writeprocedure; and invoking the determined optimum write procedure inresponse to determining the optimum write procedure, wherein thedetermining is based at least in part on: an expected writing time foreach of the plurality of candidate write procedures; an expected timeremaining until a next write operation; and an expected transaction sizeof the next write operation.